Axial type pump with stationary cylinders



W. FERRIS March 13, 1956 AXIAL TYPE PUMP WITH STATIONARY CYLINDERS l5 Sheets-Sheet 1 Filed Aug. 15, 1952 INVENTOR WALTER FERRIS AT OR NEY March 13, 1956 w. FERRIS 2,737,894

AXIAL TYPE PUMP WITH STATIONARY CYLINDERS Filed Aug. 15, 1952 15 Sheets-Sheet 2 FIG. 2

INVENTOR 1 WALTER FERRIS W. FERRIS March 13, 1956 AXIAL TYPE PUMP WITH STATIONARY CYLINDERS 15 Sheets-Sheet 3 Filed Aug. 15, 1952 INVENTOR WALTER FERRIS ATTORNEY March 13, 1956 W. FERRIS AXIAL TYPE PUMP WITH STATIONARY CYLINDERS Filed Aug. 15, 1952 15 Sheets-Sheet 4 INVENTOR WALTER FERRIS ATTORNEY March 13, 1956 w. FERRIS AXIAL. TYPE PUMP WITH STATIONARY CYLINDERS Filed Aug. 15, 1952 15 Sheets-Sheet 5 INVENTOR WALTER' FERRIS March 13, 1956 w. FERRIS 2,737,394

AXIAL TYPE PUMP WITH STATIONARY CYLINDERS Filed Aug. 15, 1952 15 Sheets-Sheet 6 FIG.

FIG. 25

INVENTOR WALTER FERRIS AT ORNEY March 13, 1956 w. FERRIS 2,737,894

AXIAL TYPE PUMP WITH STATIONARY CYLINDERS Filed Aug. 15, 1952 15 Sheets-Sheet 7 FIG. 7

I' I03 o FIG. 8 n4 k m a 1 7/4 /////A |23- so m ll I30- I' I I H7 INVENTOR WALTER FERRIS ATTORNEY AXIAL TYPE PUMP WITH STATIONARY CYLINDERS 4 INVENTOR 49 a so V D I BViALTER FERIRIS CP- 4| 12L 45 F- ATTORNEY W. FERRIS March 13, 1956 AXIAL TYPE PUMP WITH STATIONARY CYLINDERS 15 Sheets-Sheet 9 Filed Aug. 15, 1952 WALTER FERRIS BY W :TORNEY March 13, 1956 w. FERRIS 2,737,894

AXIAL TYPE PUMP WITH STATIONARY CYLINDERS Filed Aug. 15, 1952 15 Sheets-Sheet 10 FIG. l4 l3 II I53 I56 I55 I56 F 3 a '66 FIG. l2

IG. 53 l6? \yssd I65 23 INVENTOR WALTER FER RIS ATTORNEY W. FERRIS March 13, 1956 AXIAL TYPE PUMP WITH STATIONARY CYLINDERS l5 Sheets-Sheet l3 Filed Aug. 15, 1952 INVENTOR WALTER FER R|$ B MPYM ATTORNEY 2n NN 6- m) m I March 13, 1956 W. FERRIS AXIAL TYPE PUMP WITH STATIONARY CYLINDERS Filed Aug. 15, 1952 FIG. 23

Z217, (L1 23s '23 v 274 271 273 1% 275 l8l I84 |77{ we ,7. 7 W |ans4 fi i/fl 3 2 v 7 300 s |/77{ 5 L7 304 7 [8! P17 we I85 we INVENTOR WALTER FERRIS 15 Sfieets-Sheet 14 ATTORNEY March 13, 1956 w, R s 2,737,894

AXIAL TYPE PUMP WITH STATIONARY CYLINDERS Filed Aug. 15, 1952 15 Shoots-Sheet 15 INVENTOR WALTER FERRIS ATTORNEY United States Patent "ice AXIAL TYPE PUMP WITH STATIONARY CYLINDERS Walter Ferris, Milwaukee, Wis., assiguor to The Oilgear Company, Milwaukee, Wis., a corporation of Wiscousin Application August 15, 1952, Serial No. 304,477 16 Claims. (Cl. 103-5) This invention relates to multiple piston axial type pumps for pumping liquid at high pressures, the liquid usually being employed to energize hydraulic motors. The pump includes a cylinder barrel or block in which the pistons and cylinders are arranged in one or more circular rows about a central axis and are usually parallel to each other and to the axis. In a pump embodying the invention, the cylinder block is non-rotatable, such as by being fixed to or forming part of the main frame, and the pistons are reciprocated by a driving plate or cam which is inclined to and fixed for rotation with a drive shaft the axis of which coincides with the axis of the cylinder block. However, certain features of the invention may also be embodied in conventional types of axial pumps in which the cylinder barrel or block is rotatable and the pistons are reciprocated by a driving plate or cam which is mounted in the casing and is inclined at an angle to the axis of the cylinder barrel.

The present invention has as an object to provide a pump capable of discharging a larger volume ofliquid at high pressures than the pumps which were heretofore commercially available.

Another object is to provide a pump in whichthe flow of liquid to and from each cylinder is controlled by a separate valve, and the several valves are operated in timed sequence with the strokes of the corresponding pistons.

Another object is to provide a pump having each cylinder ported during the greater part of its stroke through a mechanically actuated valve of ample capacity to take the maximum flow, but ported during the end portions of each stroke only through auxiliary valves especially adapted to prevent shocks at the opening and closing of discharge port.

Another object is to provide a pump in which a separate valve controls each cylinder and each valve will not connect its cylinder to the discharge port until after the piston in its cylinder has created a pressure higher than the pressure in the discharge port. 7

Another object is to provide a machine of the above type with improved means for transmitting motion between the shaft and the pistons.

Other objects and advantages will appear from the description hereinafter given of a pump in which the invention is embodied.

The invention is exemplified by the pump shown in part schematically in the accompanying drawings in which the views are as follows: a

Fig. 1 is in part an elevation of and. in part a longitudinal vertical central section through a pump in which the invention is embodied, the plane of the view being indicated by the line 1-1 of Fig. 2. 1

Fig. 2 is a transverse vertical section taken on the line 2-2 of Fig. 1 but drawn to a larger scale.

Fig. 3 isa transverse vertical sectional view illustrating the trunnions for a counterweight and also for a wobble plate which efiiects reciprocation of the pumping pistons in response to rotation of a drive shaft, the View 2,737,894 Patented Mar. 13, 1956 being taken on the line 3-3 of Fig. 1 but drawn to approximately the same scale as Fig. 2.

Fig. 4 is a sectional plan view taken through the pumping portion of the pump on the irregular line 4-4 of Fig. 2.

Fig. 5 is a sectional plan view taken through the other end portion of the pump on the line 5-5 of Fig. 3.

Fig. 6 is an end view of the pump with a cover plate removed and illustrates the mechanism for shifting the valves which control the main flow of liquid to and from the pump cylinders, the view being taken on the line 6-6 of Fig. 1 but drawn to approximately the same scale as Fig. 2. t

Fig. 7 is a view showing two check valves through which liquid may flow to and from a cylinder when the valve which controls the main flow of liquid to and from that cylinder is closed, the view being taken in the same plane as Fig. 1 but drawn to a considerably larger scale.

Fig. 8 is a view illustrating how each piston is connected to the wobble plate which efiects reciprocation of the pistons, the view being taken in the same plane as Fig. 1 but drawn to approximately the same scale as Fig. 7.

Fig. 9 is a diagram of the hydraulic circuit in the pumping portion of the pump, only four of the pistons and the valves associated therewith being shown.

Fig. 10 is a view of the front face of the wobble plate, the view being taken on the line 10-10 of Fig. 1 but drawn to a larger scale.

Fig. 11 is a rear face view of an element which engages the front face of the wobble plate and functions both as a hydraulic thrust bearing and as a valve, the view being taken on the line 11-11 of Fig. 1 but drawn to approximately the same scale as Fig. 10.

Fig. 12 is a section taken through a part of the thrust bearing shown in Fig. 11 and through a rocker which supports the thrust bearing and is tiltable to vary the displacement of the pump, the view being drawn to approximately the same scale as Fig. 11 and taken in the plane indicated by the line 12-12 of Fig. 5 and also indicated by the line 12-12 of Fig. 11.

Fig. 13 is a developed face view of a liner through which forces are transmitted between the arcuate face of the rocker and a driving head through which rotation is transmitted from the drive shaft to the rocker and the wobble plate, the view being indicated by the arcuate line 13-13 of Fig. 12.

h Fig. 14 is a section taken on the line 14-14 of Fig. 13. Fig. 15 is a transverse sectional view showing a part of the mechanism for tilting the rocker and for also tilting in the opposite direction a counterweight which is provided to. neutralize the unbalanced centrifugal forces in the rocker and the wobble plate, the view being taken on the irregular line 15-15 of Fig. 1 but drawn to approximately the same scale as Figs. 2-6.

Fig. 16 is a longitudinal vertical sectional view showing the rocker and a part of the tilting mechanism, the plane of the view being indicated by the line 16-16 of Fig. 5 and by the line 16-16 of Fig. 15.

Fig. 17 is a section through a mechanism for applying spring force to the counterweight, the view being taken on the line 17-17 of Fig. 5.

Fig. 18 is a section taken on the line 18-18 of Fig. 17.

Fig. 19 is a section through the driving head and certain adjacent parts taken on the irregular line 19-19 of Fig. 15 and showing the hydraulic motors for tilting the rocker and the counterweight.

Fig. 20 is a longitudinal vertical section through the portion of the pump which is shown in elevation in Fig. 1, the view being taken on the irregular line 20-20 of Fig. 5 and showing a part of the mechanism for controlling the hydraulic motors shown in Fig. 19.

Fig. 21 is a fragmentary plan view taken on the irregular line 2121 of Fig. 20.

Fig. 22 is a transverse section taken on the line 2222 of Fig. 20.

Fig. 23 is a vertical transverse section taken on the line 2323 of Fig. 20 but drawn to a larger scale.

Fig. 24 is a diagram of the hydraulic circuit in the driving portion of the pump.

Fig. 25 is a diagrammatic view of the piston recipocating mechanism.

The pump illustrated is so large and the scale of the drawings is necessarily so small that some clearances and the sizes of some parts had to be exaggerated and some features, such as sealing means and bearings for rotating parts, had to be omitted.

General arrangement The pump has the greater part of its mechanism arranged Within a casing 1 which has an end head 2 rigidly attached to and closing its front end and a cylinder block 3 closely fitted in and rigidly attached to its rear end portion. Casing 1 is adapted to be mounted upon a reservoir 4 which has not been shown in connection with casing 1 but has been shown schematically in Fig. 9.

A drive shaft 5 extends through casing 1 upon approximately the horizontal centerline thereof and is rotatably supported by a bearing 6 carried by end head 2, by a bearing 7 carried by cylinder block 3 at the front end thereof and by a bearing 8 carried by cylinder block 3 at therear end thereof, bearings 7 and 8 being spaced apart by a spacer tube 9 arranged upon shaft 5.

Cylinder block 3 has a plurality of cylinders 10 formed therein in a circular row concentric with shaft 5. A piston 11 is fitted in each cylinder 10 and is connected by a connecting rod 12 to a non-rotating thrust member or wobble plate 13 which is rockably supported at its center upon a stationary hollow ball 14 the center of which is on the axis of shaft 5 and through which shaft 5 extends with sufficient clearance to prevent the shaft from contacting the ball. As shown, ball 14 is provided with an annular flange 14 which is rigidly secured to the front end of cylinder block 3. Wobble plate 13 is provided with an annular split bearing 13 which is closely fitted therein and has an internal spherical surface complementary to and closely fitted upon ball 14 to rock thereon. The means for lubricating ball 14 has not been shown as it forms no part of the present invention.

Rotation ofwobble plate 13 is prevented by a universal joint the ring 15 of which has wobble plate 13 pivotally connected thereto at diametrically opposite points by two pins 16 as shown in Figs. 1 and 3. Ring 15 is pivoted at points spaced 90 from pins 16 upon two pins 17 (Figs. 3 and 5) arranged in the bifurcated ends of two arms 18 'each of which is slidably supported in a bracket 19 carried by easing 1. The extended axes of pins 16 and 17 pass through the center of ball 14.

Wobble plate 13 is restrained from axialrnovernent against the thrust of pistons 11 by a rocker '20 which is arranged within a driving head 21. As will presently be more fully explained, rocker 20 and driving head 21 are fixed for rotation with shaft 5 and are restrained from axial movement. The forces which prevent axial movement of wobble plate 13 are transmitted through a holdup element 22, which has been shown as engaging the fiat front face of wobble plate 13 and which is arranged in a recess 23 extending into rocker 20 from the fiat rear face thereof, and through a plurality of piston shoes 24 each of which is associated with a connecting rod 12 and bears against the fiat rear face of rocker 20 radially outward from element 22. The front face of rocker 20 and the rear face of driving head 21 are cylindrcal and are accurately machined to radii struck from the center of ball 14. Concavo-convex liners (not appearing in Fig. 1) are closely fitted between the cylindrical surfaces to transmit axial forces from one to the other and to permit relative radial movement therebetween.

The arrangement is such that rocker 20 may be swung about the center of ball 14 either upward or downward in respect to Fig. 1 to accurately adjusted positions at one side or the other of the neutral position shown in Fig. 1. Swinging rocker 20 away from its neutral position causes its rear face to be inclined to the axis of shaft 5 and to gyrate about the shaft axis as the shaft and rocker 20 rotate. Since shoes 24 bear against the rear face of rocker 20, gyration of that face causes wobble plate 13 to pivot upon pins 16, ring 15 to pivot upon pins 17 and wobble plate 13 to wobble upon ball 14, thereby effecting reciprocation of pistons 11.

The pumping mechanism Cylinder block 3 is cylindrical and is closely fitted in a bore 25 formed in the rear end portion of casing 1. As shown in Figs. 1, 2 and 4, each of cylinders 10 has a piston valve 26 associated therewith and the several valves are arranged in a circular row concentric with the row of cylinders 10. Each valve 26 is preferably fitted in a ported sleeve which is arranged in a bore formed in cylinder block 3 but in order to simplify the drawings each valve 26 has been shown fitted for reciprocation in a bore 27 which is formed in cylinder block 3 and has three annular grooves or ports 28, 29 and 39 formed in its wall. Each port 28 communicates through a passage 31 (Fig. 2) with one of the cylinders 10. Each port 29 communicates through a passage 32 with an annular passage 33 which is formed in the wall of the bore 25 in casing 1 and communicates with a passage 34 (Fig. 4) by means of which the pump may be connected to one side of a hydraulic circuit. Each port 36 communicates through a passage 35 with an annular passage 36 which is formed in the wall of bore 25 and communicates with a passage 37 (Fig. 4) by means of which the pump may be connected to the other side of the hydraulic circuit.

Valves 26 may be made large enough to permit cylinders 10 to be filled with liquid from an adjacent reservoir in response to retraction of pistons 11 but the size of valves 26 and the forces required to reciprocate them may be considerably reduced if the pump is supercharged at a pressure, such as 35 p. s. i., which is relatively low but is high enough to obtain the necessary velocity of the liquid passing through the valves 26 on the intake side of the pump.

As shown schematically in Fig. 9, liquid for supercharg'ing the pump may be supplied by an auxiliary pump 40' which draws liquid from reservoir 4 and discharges it through a channel 41, a selector valve 42 and either a channel 43 into passage 33 or through a channel 44 into passage 36. Since the pump may be employed in a differential hydraulic circuit, a low pressure relief valve 45 is connected to channel 41 and discharges into reservoir 4 so that whenever liquid is returned to the main pump in excess of the liquid required to fill cylinders 10, the excess'liquid may be exhausted through relief valve 45.

Since the pressure required to supercharge the main pump is low, supercharge pump 40 may be of a constant displacement type and the liquid discharged by it in excess of the liquid required to fill cylinders 10 may be exhausted through relief valve 45. But preferably the supercharge pump is a constant pressure pump. That is, a pump which will discharge liquid at a predetermined maximum rate. until it creates a predetermined pressure and then it willautomatically reduce its displacement until it is delivering just enough liquid to maintain that pressure substantially constant, suchas the supercharge pump shown in PatentNo. 2,484,337.

Selector valve 42 includes a body 46 which is fastened to casing 1 and has an axial bore 47 and three annular grooves or ports 48, 49 and 50 formed in the wall of bore 47. Port 48. is connected by channel 41 to pump 40, port 49 is connected by channel 43 to passage 33 and port 50 isconnect'ed by channel 44 to passage 36. Communication between port 48 and ports 49 and 50 is controlled by a valve plunger 51 which is fitted in bore 47 and has two ducts 52' and 53 extending into it from its opposite ends and then extending radially outward into communication with ports 49 and 50 respectively.

The arrangement is such that, when high pressure is created in passage 33, liquid will flow therefrom through channel 43, port 49 and duct 52 to one end of bore 47 and will shift plunger 51 into the position shown and plunger 51 will open port 50 to port 48 so that liquid can flow from pump 40 through channel 41, selector valve 42 and channel 44 into passage 36 and, when high pressure is created in passage 36, liquid will flow therefrom through channel 44, port 50 and duct 53 to the other end of bore 47 and will shift plunger 51 into its other position and plunger 51 will open port 49 to port 48 so that liquid can flow from pump 40 through channel 41, selector valve 42 and channel 43 into passage 33.

Port 48 in valve 42 is also connected by a passage 54 to an annular passage 55 which extends around cylinder block 3 and has been shown as being formed in part in casing 1 and in part in cylinder block 3. Passage 55 is thus continuously supplied with supercharging liquid.

The mechanism for shifting valves 26 has been shown in Figs. 1, 4 and 6 as being arranged within a cylindrical housing 58 which is attached to the rear end of cylinder block 3 and is closed at its rear end by a cover plate 59. Each of valves 26 has a universal joint 60 fixed to its rear end and connected by linkage 61 to one of the several arms 62 of a valve actuator 63 which is journaled as by means of bearings 64 upon a tubular cam 65 which is fixed upon the rear end portion of shaft 5. The axis of the outer periphery of cam 65 is inclined to the axis of the inner periphery thereof so that actuator 63 is inclined to the axis of shaft 5. 1

Actuator 63 is pivoted at diametrically opposed points on its horizontal center line to a ring 66 by two pins 67. Ring 66 is pivoted at diametrically opposite points on its vertical center line upon two pins 68 carried by two arms 69 which are supported in two brackets 70 carried by housing 58. The arrangement is such that, when shaft is rotated, cam 65 will cause actuator 63 to pivot upon pins 67, ring 66 to pivot upon pins 68 and actuator 63 to wobble about the intersection of the axes of shaft 5 and pins 67.

Cam 65 is fixed upon shaft 5 in such a position that, when rocker 20 is adjusted to cause wobble plate 13 to be inclined to the axis of shaft 5 as previously explained, the plane of valve actuator 63 will be spaced 90 from the plane of wobble plate 13. The arrangement is such that, when the pump is pumping liquid and any piston 11 is at either end of its stroke, the valve 26 associated with the cylinder containing that piston will be in its closed position and will be blocking the port 28 leading to that cylinder as shown in Fig. l. Instantly thereafter, both the piston and the valve start to move but the piston will be moving at its slowest speed while the valve will be moving at its highest speed so that the valve will quickly open port 28. The piston will accelerate and the valve will decelerate until the piston is at half stroke at which time the valve will be fully open as shown in Fig. 4. Then the piston will decelerate and the valve will accelerate until the piston reaches the other end of its stroke at which time the valve will have closed port 28 as shown in Fig. 1.

In Fig. 25 driving head 21 has been shown in the same position as in Fig. 1 but rocker 20 has been shown as having been swung downward in respect to Fig. 1 so that its rear face is inclined to the axis of shaft 5 and will gyrate about the shaft axis when shaft 5 and rocker 20 are rotated. The thrust of pistons 11 holds piston shoes 24 against the rear face of rocker 20 and thereby maintains wobble plate 13 parallel to the rear face of rocker 20. Two diametrically opposite points at which piston shoes 24 contact the rear face of rocker 20have been indicated at A and B, point A being the contact point farthest from cylinder block 3 and point B being the contact point nearest to cylinder block 3.

With rocker 20 in the position shown in Fig. 25, the upper piston designated 11 is at the end of its outstroke and its shoe 24 is in contact with the rear face of rocker 20 at point A. Cylinder block 3 contains an odd number of cylinders so that no two pistons are diametrically opposite each other but, for the purpose of this explanation, a piston 11 has been shown diametrically opposite piston 11 in Fig. 25 with the shoe 24 of the lower piston 11 in contact with the rear face of rocker 20 at point B, in which position piston 11 is at the end of its in-stroke.

When shaft 5 is rotated in the direction indicated by the arrow on Fig. 25, driving head 21 and rocker 20 will rotate with it and the rear face of rocker 20 will slide across the faces of the several piston shoes 24. During the first half-revolution of rocker 20 from the position shown in Fig. 25, its rear face will move the shoe 24 of upper piston 11 rearward or inward harmonically until point B comes into alinement with that shoe at which time piston 11 will have been moved to the end of its in-stroke or into a position corresponding to the position of piston 11 shown in Fig. 25.

During the next half-revolution of rocker 20, its rear face will permit the shoe 24 of piston 11 to be moved forward harmonically. If the pump is supercharged as shown, piston 11 will be moved forward or outward by the supercharge pressure. If the pump is not supercharged, piston 11 will be drawn forward or outward by wobble plate 13. -In either case, piston 11 will be moved forward or outward harmonically until point A comes into alinernent with the shoe 24 of that piston at which time piston 11 will have made a complete reciprocation and will be in the position shown in Fig. 25. Con tinuous rotation of rocker 20 will cause continuous reciprocation of the piston.

All of the pistons 11 are reciprocated in the same manner, the pistons whose shoes 24 are in contact with that half of rocker 20 which is the far half in respect to Fig. 25 being forced progressively rearward or inward and the pistons whose shoes 24 are in contact with that half of rocker 20 which is the near half in respect to Fig. 25 being moved progressively forward or outward.

As each piston 11 starts to move inward or rearward in its cylinder, the valve 26 associated with that cylinder will move in a direction to connect its port 28 to its port 29 and, as each piston 11 starts to move outward or forward in its cylinder, the valve 26 associated with that cylinder will move in a direction to connect its port 28 to its port 30. The inward moving pistons will discharge liquid from their cylinders through passages 31, ports 28, valve bores 27, ports 29 and passages 32 into annular passage 33 and thence through passage 34 to one side of an external circuit. The cylinders containing outward moving pistons will be supplied with liquid through passages 31, ports 28, valve bores 27, ports 30 and passages 35 from annular passage 36. Part or all of the liquid required to fill the cylinders may be supplied to passage 36 through passage 37 from the external circuit or a part or all of the liquid required to fill the cylinders may be supplied to passage 36 through passage 44, selector valve 42 and passage 41 from supercharge pump 40.

If rocker 20 is swung upward from its neutral position, the pump will function in the above described manner except that the movement of the pistons will be reversed, the pistons will discharge liquid into annular passage 36 and the cylinders will be supplied with liquid from annular passage 33.

When the pump is creating a high pressure and a piston starts to move inward, the liquid in the cylinder containing that piston is initially under a low pressure if the pump is supercharged, or it is under a negative pressure and the cylindermay not be completely filled with liquid if the piston has to draw liquid into its cylinder'frorn a reservoir, but the discharge passage 33 or '36 contains liquid at the high pressure. Therefore, if each valve '26 opened the associated cylinderto the discharge passage at the instant that the piston in that cylinder started to move inward, the high pressure in-the discharge passage would cause liquid to flow therefrom into the cylinder and cause a shock with resultant noise and energy loss. These shocks in pumps now in use often disintegrate the metal in the port walls.

In order to eliminate such shocks and noise, each -valve 26-is soproportioned-that it does not open the assooiated cylinder to the .discharge passage until after the piston in that cylinder has moved inward far enough to .create in its cylinder a pressure approximately as-high as the pressure in the discharge passage and each cylinder is provided with anoutlet check valve 71 through which the piston may discharge liquid before the valve 26 opens.

If the pump is reversible as shown, each valve 26 must ;be so proportioned that it will not open its port 28 to either "its port 29 or its port 3t until after it has moved a predetermined distance in one direction or the-other from its neutral position. In that case, it is preferred to provide each cylinder 10 .with an inlet check valve 72 :through which, as the piston in that cylinder moves out- .ward during the first part of intake stroke, liquid may flow to the cylinder until the valve 26 associated with that cylinder has moved far enough to connect that cylinder t the passage 33 or 36 which at .that time is the inlet passage. 'If such a check valve be not provided, the cylinder is temporarily starved at the beginning of the instroke, and gas maybe formed in the liquid in the cylinder.

While any suitable type .of check valve will sufiice, check valves 71 and 72 preferably are so constructed that .eachmay be readily inserted into and removed from cylinder block 3. As shown in Fig. '7, the check valves 71 and 7 2 for ,each cylinder are arranged, respectively, in two bores 73 and 74 formed in cylinder block 3 at the rear of that cylinder. Check valve 71 includesa body 75, which is threaded into bore 73 and has an axial bore '76 forrned therein, and an annular valve seat 77 the opening through which is concentric with bore 76 and communicates with cylinder 10. Bore 76 has a valve plunger 78 fitted therein and urged against valve seat 77 by a spring 79. -Body 7.5 also has formed in its outer periphery intermediate its ends a cannelure 8 0 through which liquid may flow tocheck valve 72 as will presently be explained. The inner part of bore 73 between body 75 and valveseat -7 7 communicates through a passage 81 with an annular passage 82 which is formed in casing 1 and extends around cylinder block 3. Suitable means are provided for subjecting the spring end of plunger 78 to the pressure prevailing in passage 82, such as a groO e 83 formed in 'th e. periphery of plunger 78.

As shown in Figs. ,1 and 9, annular passage 82 is adapted to be connected to either passage 33 or passage 36 under the control of an automatic selector valve 84 which is fitted in a bore 35 formed in a valve body 86 attached to casing 1. Bore 85 has three annular grooves or ports .87, 88 and 89 formed in the wall thereof. Port 87 is connected to passage 82 by a passage 90, port 83 is connected to passage 33 by a passage 91 and port 89 is connected to passage 36 by a passage 92. Valve 84 has two ,ducts 93 and 94 extending into it from its opposite ends and then extending radially outward into communication with ports 88 and 89 respectively.

The arrangement is such that, when high pressure is created in passage 33, liquid will flow therefrom through passage 91, port 88 and duct 93 into the left end of bore 35 and will move valve 84 against the right end of bore 85 in h ch Pos t on a e 8 i l o n c pa a e 2 t0 passage '33 through passage 90, valve body 86 and pas- {8 sage 91 and, when high pressure is created in passage 36 liquid ,will flow therefrom through passage 92, port 89 and duct 94 into the right end of bore and will move valve 84 against the left end of bore 85 in which position valve 84 will connect passage 82 to passage 36 through passage 90, valve body ;86 and passage 92.

Referring again to Fig. 7, check valve 72 includes a body 95 which ,is threaded into bore 74 and has a bore 96 extending into it from its inner end and a smaller bore '97 extending farther-into it from the end of'bore 96. A valve plunger 98 is fitted in bore 96 and is urged by a spring 99 against 'theshoulder formed at the junction of bores 96 and 97, thereby normally preventing flow of "liquid from one bore 'tothe other.

Valve body 95 also has two cannelures 100 and 101 formed in its peripheral surface and spaced from each other. Cannelure 100 communicates with cylinder 10 through a passage 102 and-it communicates with the opposite ends of bore 96 through two sets of holes 103 and 104 respectively. Cannelure 101 communicates with bore 97 through a plurality of holes 105 and it is connected to supercharge passage 55 bya passage 106 which is intersected by bore 73 in the plane of cannelure 80.

The arrangement is such that the supercharge pressure, which is constantly maintained in passage 55, extends through passage 106, cannelure 101 and holes M5 into bore 97 and tends to move plunger 93 to open position but any pressure in cylinder 10 extends therefrom through passage 1392, cannelure andholes 193 into the spring end of bore '96 and assists spring 99 in holding plunger 98 in its closed position. When piston 11 is retracted, the pressure in cylinder 10 will drop until the force exerted upon plunger 98 by spring 99 and by any pressure in cylinder i is less than the force exerted upon plunger 98 by the supercharge pressure. Then the preponderance of force exerted upon plunger "98 by the supercharge pressure will move plunger 98 to its open position and liquid will flow from .supercharge passage 55 through passage 106, cannelure 101, holes 105, bore 97, holes 104, cannelure 100 and passage 162 into cylinder It) and will fill cylinder 10 with liquid as fast as piston '11 is retracted.

Referring now to Fig. 9 and assuming that the pump is adjusted to cause the pistons 11 to discharge into passage 33 as previously explained, the pistons 11 which are moving inward but are not near either the inner or the outer ends of t eir strokes are represented by the piston 1i and the cylinder containing that piston and the valves associated therewith are indicated by their reference numerals with the exponent (1 added thereto. The pistons which are near the inner ends of their strokes are represented by the piston "11 and the cylinder containing that piston and the valves associated therewith are indicated by their reference numerals with the exponent 'b added thereto. The pistons 11 which are moving outward but are not near either the inner or the outer ends of their strokes are represented by the piston 11 and the cylinder containing that piston and the valves associated therewith are indicated by their reference numerals with the exponent 0 added thereto. The pistons 11 which are near the outer ends of their strokes are represented by the piston 11 and the cylinder containing that piston and the valves associated therewith are indicated by their reference numerals with the exponent d added thereto.

During the in-stroke .of a piston 11 as indicated by the lar e arrow thereon, it will discharge liquid tron its cylinder 10 through passage 31 valve bore 27*, passage 32 and discharge passage 33 to the external circuit as indicated by the small arrows on those passages. At the same timeQeach piston 11 is being retracted, as ndica d y t ge arrow the eon, an liquid i being returned from the external circuit into passage 36. Since pump 4.0 is maintaining pressure in passage 36 ,as indicated in Fig. 9 and as previously explained,

the pressure in passage 36 will cause each cylinder 10 to be supplied with liquid through passage 31, valve bore 27 and passage 35 from passage 36 as indicated by the small arrows on those passages, valves 26 and 26 being at this time open wide enough to permit liquid to flow freely from cylinder 10 to paslsage 33 and into cylinder 10 from passage 36.

Just before each piston 11 reaches the end of its in- .stroke, the valve 26 associated with that piston closes, as indicated by the position of valve 26 and the piston continues to move inward as indicated by the full arrow on piston 11 After valve 26* closes, piston 11 Wlll discharge liquid from its cylinder 10'" through check valve 71', passages 81, 82 and 90, valve body 86 and passages 91 and 33 to the external circuit, as indicated by the full arrows on those passages, until the contact point B (Fig. 25) on the rear face of rocker 20 comes into alinement with the shoe 24 on that piston at which timethe piston is at the end of its in-stroke as previously explained.

Each piston 11 starts to retract, as indicated by the dotted arrow on piston 11', the instant that contact point B moves out of alinement with the shoe 24 of that piston. At the end of the in-stroke, some liquid at pump pressure remains in the cylinder and, if the cylinder were opened to the intake the instant that the piston started to retract as is the case in conventional pumps, the energy required to compress that liquid to pump pressure would be wasted. In the present case, the valve 26 associated with that cylinder remains closed until shaft has rotated through a predetermined angular distance. During that time, the pressure in the cylinder reacts against the inclined rear face of rocker 20 and, the instant that contact point B on the rear face of rocker 20 moves beyond the axis of the shoe 24 of the piston in that cylinder, the liquid in the cylinder expands and assists in rotating shaft 5, thereby regenerating a large part of the energy required to compress to pump pressure the liquid remaining in each cylinder at the end of the ins'troke of the piston in that cylinder.

As soon as the liquid remaining in cylinder 11 has expanded to such an extent that the pressure in cylinder 11 is enough less than the supercharge pressure to permit check valve 72 to open, liquid will flow from supercharge passage 55 through passage 106 check valve 72" and passage 102 to cylinder 11 and keep it filled with liquid until shaft 5 has rotated through an angular distance great enough to cause valve actuator 63 to open valve 26 and thereby permit the cylinder to be filled with liquid from passage 36 as explained above and as shown in Fig. 9 by the arrows which indicate the flow of liquid into cylinder 10 Just before each piston 11 reaches the end of its outstroke, the valve 26 associated with that piston closes, as indicated by the position of the valve 26 and the piston continues to move outward as indicated by the dotted arrow on piston 11 After valve 26 closes, liquid is supplied to cylinder 10 from supercharge passage 55 through passage 102 check valve 72 and passage 106 as indicated by the dotted arrows on those passages.

Each piston 11 starts to advance, as indicated by the full arrow on piston 11 instantly after it reaches the end of its out-stroke but valve 26 is closed at that instant so that piston 11 cannot discharge liquid from cylinder 10 until after it has created therein a pressure somewhat higher than the pressure in passages 33 and 82. Then check valve 71 will open and piston 11 will discharge liquid from its cylinder 10 through check valve 71 passages 81 82 and 90, valve body 86 and passages 91 and 33 to the external circuit, as indicated by the small full arrows on those passages, until piston 11 has advanced a short distance and then valve 26 will open and permit the piston to discharge liquid into passage 33 as explained above and as shown by the discharge of liquid from cylinder 10*.

10 The piston and wobble plate assembly Pistons 11 may be retracted either by supplying liquid to cylinders 10 at a sufliciently high pressure or by connecting pistons 11 to wobble plate 13 by suitable linkages such as the connecting rods 12. As shown in Fig. 8, each piston 11 has a spherical head 109 fixed to its outer end and fitted into a socket 110 formed upon one end of a short push rod 111 having a spherical head 112 formed upon its other end. Head 112 is fitted in a spherical socket 113 which has a shank 114 formed integral therewith and rigidly secured in wobble plate 13. An annular socket 115 is fitted upon the outer spherical surface of socket 113 and is connected to a sleeve 116 which encloses head 109 and socket 110 and has an annular inward flange 117 on its rear end. Flange 117 is engaged by a spring 118 which urges an annular spherical socket 119 against the rear face of head 109 and thereby prevents separation of ball and socket joint 109-110 and separation of ball and socket joint 112-113.

The arrangement is such that piston 11 may be drawn outward or forward by a retraction force transmitted thereto through its head 109, socket 119, spring 118, flange 117, sleeve 116 and sockets 115 and 113 from wobble plate 13, and piston 11 may be forced inward or rearward by a pumping force transmitted thereto through its head 109, rod 111, head 112 and socket 113. The pumping force is transmitted from rocker 20 to socket 113 partly through wobble plate 13 and partly through a shoe to be presently described.

In order to provide hydraulic thrust bearings in the ball and socket joints and to provide liquid for lubrication and other purposes, a recess 120 is provided between head 109 and socket 110, such as by flattening the end of head 109, and piston 11 is provided with an axial duct 121 which extends from recess 120 through piston 11 into communication with cylinder 10 (see Fig. 7) so that liquid can flow from cylinder 10 into recess 120. A recess 122 is similarly provided between head 112 and socket 113 and is supplied with liquid through a duct 123 which extends through ball 112 and rod 111 into communication with recess 120.

When pressure prevails in cylinder 10, liquid spreads over the spherical mating surfaces of the heads and the sockets and forms lubricating films therebetween. The area of each film into which pressure can extend should be limited and this may be accomplished by making socket 110 relatively short and by providing a suitably drained limit groove 124 in head 112. Any pressure in cylinder 10 will extend through duct 121 into recess 120 and through duct 123 into recess 122 so that the pressure in recesses 120 and 122 is the same as in cylinder 10. The pressure in the recesses will extend therefrom into the films of liquid between the mating surfaces of the balls and sockets. The film pressure at the edge of each recess will be the same as the pressure in the recess and will be substantially zero at edge of socket 110 and at the edge of groove 124. The liquid in each of recesses 120 and 121 acts as a liquid bearing between the ball and its socket and the area of each recess and the area of the film of liquid are such that the greater part of the pumping force is transmitted through the liquid in the recesses and the films containing pressure and only a small part of the pumping forces is transmitted through the films which have little or no pressure therein.

The pressure in the recess and in the film of liquid between each head and its socket tends to move the head away from its socket but the area of each recess and the area of the film containing pressure are so proportioned that the force exerted by the liquid upon each head is slightly less than the force exerted upon the inner end of the piston by the liquid in the cylinder.

A part of the pumping force required to advance piston 11 on a working stroke is transmitted from rocker 20 to socket 113 through the shoe 24 of that piston. Shoe 

